The overall objectives of this project remains to contribute to an understanding of the mechanisms and regulation of cell-mediated immunity in man. In the present proposal immunoregulation, particularly the molecular basis for down-regulation of cell-mediated immunity, has become the major focus of this work. Because resistance to intracellular infections correlates with the level of cell-mediated immunity in several infectious diseases, including leprosy and leishmaniasis, these diseases serve as important models for gaining insight into immunoregulation in man. A major interest will be the peripheral tolerance of antigen- specific unresponsiveness in patients with lepromatous leprosy and with the cutaneous forms of leishmaniasis. For the past ten years we have described the activity, phenotype, specificity, receptors and genetic restrictions on a subset of T cells from patients with lepromatous of Th1 or Type 1 CD4 specific T cells in vitro. The major aim of this proposal is to pursue the nature of the T cells that regulate both cell mediated- immunity and unresponsiveness, and to delineate the mechanisms in molecular terms by which functional subsets of T cells and the cytokines they produce, cross-regulated one another. We propose to test the hypothesis that IL-4 and other regulatory cytokines produced by the TH2- like cells suppress IL-2 and IFN-gamma gene expression. We proposed to characterize transcriptional activator(s) regulated by IL-4, clone the transcriptional factor cDNAs and genomic DNAs and define their interactions with other known transcriptional factors, using the two- hybrid plasmid strategy for cloning genes encoding interactive proteins. We propose as well to characterize the effects of other down-regulatory cytokines, such as IL-10, TGF-beta and possibly IL-13 on suppressing transcription of the IL-2 and IFN-gamma genes. We hope further to characterize the T cell subsets that regulate cell- mediated immunity, and in particular, to characterize the immunological activity, specificity and restrictions of CD4 suppressive cells, and their relationship to TH2 helpher cells. Finally, having identified a subset of gamma, delta T cells found in healing lesions of tuberculoid leprosy that respond to mycobacteria, we propose to characterize the low- molecular weight antigen or superantigen recognized by these V delta 2, V gamma mycobacterial reactive gamma, cells which are also cytotoxic for hematopoietic tumor cells in vitro. The antigen will be purified from M. tuberculosis culture filtrates, molecularly characterized, chemically synthesized and tested for adjuvant and specific protective biological activities against tumors and infectious challenges.